Modal suppression and single-mode emission in photonic crystal coupled-cavity ring-like lasers

We have designed and fabricated a new class of photonic crystal ring-like laser structure with hexagonal shape on InGaAsP/InP semiconductor slabs by introducing nanocavities in the corners of the hexagonal ring. Different structures have been designed and fabricated by shifting the position of the nanocavity by one lattice parameter around the corners. Laser emission has been measured and characterized. The global effect of the introduction of an H1 cavity located in the six corners of a hexagonal waveguide ring-like resonator promotes a strong modal suppression compared to the ring structure without cavities. The introduction of the nanocavities reduces the many modes of the regular hexagonal ring-like structure, as finite element calculations show. Ring-like structures without cavities show multimode spectra while structures with cavities present strong mode reduction in the studied range. For a specific design of the structures with the cavities inside the hexagon area a clearly single mode emission is observed with a side mode suppression ratio higher than 20 dB.